Cane toads were introduced to Queensland in 1935 and have since spread across northern Australia. They carry potent bufadienolide toxins in parotoid glands, and native predators that evolved without them have no innate avoidance and no physiological tolerance.
Monitoring in the Victoria River district and other systems recorded steep declines in Crocodylus johnstoni following the arrival of the toad front, with some surveyed reaches losing a large fraction of their crocodiles within a few years. Dead crocodiles were found with toads in the gut. Smaller individuals are most at risk because a single toad represents a larger toxic dose relative to body mass.
The effect is not uniform. Some populations have shown partial recovery, and there is evidence from several Australian predators of learned avoidance or selection for toad-averse behaviour after the initial crash. Whether freshwater crocodile numbers return to pre-toad levels, and over what timescale, has not been settled. The species remains Least Concern overall.